I recently bought one of these capacity testers from ebay. It’s a little device that connect to battery and a resistor, and as it dumps current from battery into the resistor, it counts a mAh reading. So it’s a capacity tester. I’ve had it for few months and i’ve discharged a number of batteries with it. It seems to work but how accurate it is, I have no idea. At least it seems to get rather close to official specs of different batteries.
Using it is simple: it needs usb power and a resistor. You connect a battery with “any means necessary” - there are just wire holes. Resistor dictates how fast a battery is discharged. When a battery is connected, it first shows the battery voltage. Then, pressing up and down buttons it is possible to choose termination voltage. If only “ok” button is pressed, it chooses this automatically, using 3.0v for li-ion and 1.0v for nimh. A couple of “minus” presses and you get to 2.7 or 2.5 volts and you can measure true capacity of all li-ion batteries. You could also press “plus” and set the termination over 3.0 volts. When it starts doing it’s “thing”, it rotates mAh, current and voltage readings in the screen, and when it reaches the set termination voltage, it only flickers mAh reading in the screen, indefinitely.
The supplied 7.5 ohm resistor causes a current of about 0.5A for 4.2volt batteries, and 0.2A for nimh. The formula for current is: voltage divided by resistor ohms. I bought a few other resistors from my local electronics store, so I could measure my little 10180 li-ions, which didn’t like the 0.5A discharge current. I also connected an mp3 player as well as a flashlight as a load, and it seemed to work ok. One just has to be aware of the max 3 amp rating…
So here are some of my measurements that I did with this device:
4 x 2000mAh eneloop AA (2009): 1470, 1505, 1505, 1512mAh (1A discharge to 0.9v)
2 x 2000mAh eneloop AA (2013): 1763, 1798 mAh (1A discharge to 0.9v)
4 x 900mAh eneloop AAA (2014): 823, 832, 837, 864mAh (0.3A discharge to 0.9v)
2 x 10180 li-ion (2014): 68, 72mAh (70mA discharge to 2.7v)
Panasonic 3400mAh 18650 (2014): 3401mAh (0.5A discharge to 2.5v)
Panasonic 2900mAh 18650 (2014): 2909mAh (0.5A discharge to 2.5v)
Keeppower 2600Mah 18650 (2013): 2665mAh (0.5A discharge to 2.7v)
Keeppower 700mAh 16340 (2013): 634mAh (0.5A discharge to 2.7v)
If somebody knows more about this device and how accurate it is, feel free to chime in.